An automatic transmission device provided with a fluid coupling that has a lockup clutch is used. Regarding the above automatic transmission device, for example, Japanese Patent Application Publication No. 2016-8687 (JP 2016-8687 A) (Patent Document 1) discloses a technique of switching a path for supplying hydraulic pressure regulated by a pressure regulation valve (secondary regulation valve 66) to the fluid coupling (torque converter 7) so as to control a state (engagement/disengagement) of the lockup clutch (lockup clutch 7a) using a hydraulic control device. Patent Document 1 also discloses a technique of supplying oil discharged from the fluid coupling to a location to be lubricated (lubrication system 69) via a lubrication oil passage (lubrication oil passage 63j) when the lockup clutch is disengaged. Additionally, Patent Document 1 discloses a technique of returning the oil drained from the pressure regulation valve during pressure regulation to a suction port of an oil pump (second oil pump 62) via a return oil passage (63k).
When the hydraulic control device of Patent Document 1 is structured to return the oil drained from the pressure regulation valve during pressure regulation to the suction port of the oil pump as well as supply the oil to a location to be lubricated, the following problem occurs. Thus, by adopting the above structure, the fluid coupling and the suction port of the oil pump are in communication with each other. For example, when the vehicle is started after being stopped for a long time, the amount of oil in the fluid coupling is small and air remains in the fluid coupling. Thus, there is a possibility of the remaining air traveling through the oil passage and flowing into the suction port of the oil pump. When air flows in the suction port of the oil pump, there is a possibility of the discharge efficiency of the oil pump decreasing and noise being generated.